[RFC v2][PATCH 8/9] intel_idle: Use ACPI _CST for selected known processors

Rafael J. Wysocki
2019-12-10T12:14:01Z

Update the intel_idle driver to get the C-states information from ACPI
_CST in some cases in which the processor is known to the driver, as long as
that information is available and the new use_acpi flag is set in the
profile of the processor in question.

In the cases when there is a specific table of C-states for the given
processor in the driver, that table is used as the primary source of
information on the available C-states, but if ACPI _CST is present,
the C-states that are not listed by it will not be enabled by default
(they still can be enabled later by user space via sysfs, though).

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
drivers/idle/intel_idle.c | 45 ++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 42 insertions(+), 3 deletions(-)

Index: linux-pm/drivers/idle/intel_idle.c
===================================================================
--- linux-pm.orig/drivers/idle/intel_idle.c
+++ linux-pm/drivers/idle/intel_idle.c
@@ -80,6 +80,7 @@ struct idle_cpu {
unsigned long auto_demotion_disable_flags;
bool byt_auto_demotion_disable_flag;
bool disable_promotion_to_c1e;
+ bool use_acpi;
};

static const struct idle_cpu *icpu;
@@ -91,6 +92,11 @@ static void intel_idle_s2idle(struct cpu
static struct cpuidle_state *cpuidle_state_table;

/*
+ * Enable this state by default even if the ACPI _CST does not list it.
+ */
+#define CPUIDLE_FLAG_IGNORE_ACPI BIT(15)
+
+/*
* Set this flag for states where the HW flushes the TLB for us
* and so we don't need cross-calls to keep it consistent.
* If this flag is set, SW flushes the TLB, so even if the
@@ -1221,9 +1227,33 @@ static void intel_idle_init_cstates_acpi
state->enter_s2idle = intel_idle_s2idle;
}
}
+
+static bool intel_idle_off_by_default(u32 mwait_hint)
+{
+ int cstate, limit;
+
+ /*
+ * If there are no _CST C-states, do not disable any C-states by
+ * default.
+ */
+ if (!acpi_state_table.count)
+ return false;
+
+ limit = min_t(int, CPUIDLE_STATE_MAX, acpi_state_table.count);
+ /*
+ * If limit > 0, intel_idle_cst_usable() has returned 'true', so all of
+ * the interesting states are ACPI_CSTATE_FFH.
+ */
+ for (cstate = 1; cstate < limit; cstate++) {
+ if (acpi_state_table.states[cstate].address == mwait_hint)
+ return false;
+ }
+ return true;
+}
#else /* !CONFIG_ACPI_PROCESSOR_CSTATE */
static inline bool intel_idle_acpi_cst_extract(void) { return false; }
static inline void intel_idle_init_cstates_acpi(struct cpuidle_driver *drv) { }
+static inline bool intel_idle_off_by_default(u32 mwait_hint) { return false; }
#endif /* !CONFIG_ACPI_PROCESSOR_CSTATE */

/*
@@ -1264,10 +1294,13 @@ static int __init intel_idle_probe(void)
pr_debug("MWAIT substates: 0x%x\n", mwait_substates);

icpu = (const struct idle_cpu *)id->driver_data;
- if (icpu)
+ if (icpu) {
cpuidle_state_table = icpu->state_table;
- else if (!intel_idle_acpi_cst_extract())
+ if (icpu->use_acpi)
+ intel_idle_acpi_cst_extract();
+ } else if (!intel_idle_acpi_cst_extract()) {
return -ENODEV;
+ }

pr_debug("v" INTEL_IDLE_VERSION " model 0x%X\n",
boot_cpu_data.x86_model);
@@ -1475,7 +1508,13 @@ static void intel_idle_init_cstates_icpu
continue;

/* Structure copy. */
- drv->states[drv->state_count++] = cpuidle_state_table[cstate];
+ drv->states[drv->state_count] = cpuidle_state_table[cstate];
+
+ if (icpu->use_acpi && intel_idle_off_by_default(mwait_hint) &&
+ !(cpuidle_state_table[cstate].flags & CPUIDLE_FLAG_IGNORE_ACPI))
+ drv->states[drv->state_count].flags |= CPUIDLE_FLAG_OFF;
+
+ drv->state_count++;
}

if (icpu->byt_auto_demotion_disable_flag) {